Green-coffee-milling machine having a capacity of fortybags of green coffee per hour; with sifter, feed-pipe suction, and afinal separate suction at the discharge hopper |
Green-coffee separator without fan; with feed elevator,discharge chutes, and motor drive. View of right-hand side and feed end |
| GREEN-COFFEE SEPARATING AND MILLING MACHINES | |
Milling
Milling machines, for cleaning the green coffee, operate on practically the same principle the world over, varying in capacity and details of construction. A popular type used in the United States has two metal cylinders, one set within the other, and revolving in opposite directions. The inner cylinder is ribbed with flanges, and the outer one is lined with wire cloth. As these cylinders revolve, the beans pass between them rubbing against themselves and the rough sides of the cylinders. This action serves to remove dirt and other foreign matter that may be clinging to the beans, and also gives them an attractive polish. An exhaust fan sucks away the dirt milled off in the process. This type of machine will mill about forty bags of green coffee in an hour.
Mixing or Blending Green Coffee
Most roasters blend the different types of coffee while green. Some blend them after they have been roasted separately. When blended before roasting, the coffees are mixed by a machine built especially for that purpose. The mixing machine in general use in all countries consists of a large metal cylinder which, in wholesale operations, is revolved by the factory's general power plant or by a separate motor. The cylinder is equipped on the inside with sets of reverse-screw mixing flanges that tumble the beans around until they are thoroughly blended; and there is usually a fan attachment to remove dust. This operation serves also to smooth down and to polish the surfaces of the beans, which adds to the style of the coffee when roasted. The average blending machine will mix from ten to twenty bags of coffee at a time. The actual mixing requires less than five minutes, but a longer period is needed for feeding and discharging. This is the last of the so-called "green-coffee operations". The next step is roasting.
Roasting by Coal, Coke, Gas, and Electricity
Coffee is roasted commercially in cylinder or ball receptacles revolving in heated chambers, the degree of heat reaching about 420° Fahr. The cylinder type of roaster is invariably used in the United States; while both the cylinder and the ball types are popular in England, France, Germany, Holland, and other foreign countries.